Strategies to obtain a single enantiomer of a compound have become important in drug discovery because often one enantiomer is an effective drug while the other enantiomer has undesirable biological activity. Ideally, an asymmetric synthesis is designed to produce only the desired enantiomer. Unfortunately, more often than not, an asymmetric synthesis cannot be designed or is prohibitively expensive.
Alternatively, the mixture of enantiomers can be separated. However, mixtures of enantiomers are difficult, and often impossible, to separate because the physical properties of the enantiomers are identical towards achiral substances and can only be distinguished by their behavior towards other chiral substances. Chromatographic methods using a chiral solid phase have been utilized to separate enantiomeric mixtures, but chiral solid supports are expensive and, typically, the resolution is poor.
An alternative method of separating enantiomeric mixtures is by reacting them with a chiral reagent. In this procedure, the mixture of enantiomers react with the chiral reagent to form diastereomers which are distinguishable from each other on the basis of their properties towards achiral substances, and therefore, can be separated by techniques such as recrystallization or chromatography. This process is time consuming and results in loss of yield because it requires two additional reaction steps (i.e., one reaction to add the chiral auxiliary to the enantiomers and another reaction to remove it after the diasteriomers have been separated).
In some instances, a chiral reagent will react much faster with one enantiomer than with the other enantiomer in the enantiomeric mixture. In this case, the enantiomer which reacts faster can be removed before the other enantiomer is formed. This method also necessitates two additional reaction steps to add the chiral auxiliary and to remove it after the separation.
The methods described above cannot always be applied successfully to a particular system, and when they can be applied, they are often expensive, time consuming and results in loss of yield. Therefore, the need exists for new methods of obtaining a single enantiomer from an enantiomeric mixture.
One embodiment of the present invention is a solid support bonded to an enzyme which selectively reacts with one enantiomer in an enantiomeric mixture.
Another embodiment of the present invention is a method of selectively reacting one enantiomer in an enantiomeric mixture. The method comprises contacting the enantiomeric mixture with an enzyme which: 1) is bonded to a solid support; and 2) selectively reacts with one enantiomer, called the xe2x80x9creactive enantiomer,xe2x80x9d in the enantiomeric mixture to form a derivative of the reactive enantiomer. The immobilized enzyme and enantiomeric mixture are contacted under conditions suitable for reacting the immobilized enzyme and the reactive enantiomer, thereby forming a product mixture comprising the unreactive enantiomer and a derivative of the reactive enantiomer.
Another embodiment is a method of separating a derivative of one enantiomer from an enantiomeric mixture. The method involves contacting the enantiomeric mixture with an enzyme which: 1) is bonded to a solid support; and 2) selectively reacts with one enantiomer in the enantiomeric mixture to form a derivative of the reactive enantiomer. The immobilized enzyme and enantiomeric mixture are contacted under conditions suitable for reacting the immobilized enzyme and the reactive enantiomer, thereby forming a product mixture comprising the unreactive enantiomer and a derivative of the reactive enantiomer. The product mixture is then treated with a separating means to separate the derivative of the reactive enantiomer from the unreacted enantiomer.
Another embodiment is an apparatus for obtaining a derivative of one enantiomer in an enantiomeric mixture. The apparatus has a reaction chamber which contains an enzyme immobilized on a solid support, a means of delivering solvent to the reaction chamber, a means of loading a sample into the reaction chamber and a vessel for collecting a sample as it exits the reaction chamber.
Reported herein is the discovery of a solid support and a method for separating a single enantiomer from an enantiomeric mixture which eliminates the need to derivatize the chiral compound with a chiral auxiliary before separating the enantiomers and does not require the use of expensive chiral solid supports.